Large consumer studies show that between 1977 and 1996 in the United States average portion sizes for key food products grew markedly (Nielsen S J, Popkin B M, JAMA 2003; 289:450-453). The actual increase of portion sizes for a number of food products is shown in the following table (from the aforementioned article by Nielsen et al.):
Increase inIncreaseFood productvolume (ml)in kcalSnacks1893Hamburgers3897French fries1568Soft/fruit drinks20049
Together with the trend of decreasing physical activity, the increase in portion sizes is believed to have contributed significantly to the obesity boom.
Apart from increasing the total calorie intake, the increase of portion size has an additional important consequence, since altering visual cues (e.g. portion size) of how much is eaten influences the intake and satiety perception. A recent study (Wansink et al., Obes Res 2005; 13:93-100) suggests that people associate the amount of consumed calories/meal volume and accompanying satiety feeling with what they believe they saw themselves eating, rather than with how much they actually ate. This implies that if people believe to have consumed a relatively small volume of food, they are likely to feel less satiated then in case they believe to have consumed a relatively large volume.
Consequently, the consumption of decreased portion sizes during dieting leaves consumers with cognitive/mental and physical perception that this reduced amount of food is insufficient. Thus, consumers are left with the nagging feeling that their stomach is still ‘empty’ and find it difficult to comply with the diet. In order to overcome this problem, nutritionists have introduced the concept of food energy density, which is defined as the number of calories per given weight of food and recommend to eat foods with a low energy density. One way to achieve this is to eat products which by nature are low in energy density (e.g. high fibre fruits and vegetables) and to avoid eating energy dense products (e.g. full-fat mayonnaise, fatty meat, cakes etc.).
Another way to decrease the energy density of foods is to dilute them with non-caloric material, e.g. water or air. A large number of literature studies have confirmed that the addition of water to lower energy density increases immediate feelings of satiety and decreases subsequent food intake. The effects of simple additions of water, however, tend to be rather short-lasting (20-60 minutes). Furthermore, the addition of water is often found to adversely affect the eating quality of the edible product.
Rolls et al., Am J Clin Nutr 2000; 72:361-8 report the results of a study that examined the effect of food volume on satiety, independent of energy density (kJ/g). The design of the study was as follows: In a within-subjects design, 28 lean men consumed breakfast, lunch, and dinner in the laboratory 1 d/wk for 4 wk. On 3 d, participants received a preload 30 min before lunch and on 1 d no preload was served. Preloads consisted of isoenergetic (2088 kJ), yogurt-based milk shakes that varied in volume (300, 450, and 600 mL) as a result of the incorporation of different amounts of air. Preloads contained identical ingredients and weighed the same. It was found that the volume of the milk shake significantly affected energy intake at lunch (P<0.04) such that intake was 12% lower after the 600 mL preload than after the 300 mL preload. Furthermore it is stated that subjects reported greater reductions in hunger and greater increase in fullness after consumption of both the 450 and 600 mL preloads than after the 300 mL preload. However, the authors also conclude that “Subjects overate compared with the control condition (4199±193 kJ) in the 300 mL (5456±196 kJ), 450 mL (5233±180 kJ) and 600 mL conditions (5054±246 kJ). Therefore, it can be concluded from this study that the consumption of the preloads failed to induce a level of satiety that resulted in the consumption of less energy.
Edible foam products of pourable or spoonable consistency are known in the art. EP-A 0 292 034 describes a foamable product consisting of a homogenized mixture of fat, protein, water, alcohol and a calcium source containing lactates and/or polyphosphate. It is observed that foaming of the foamable product can be performed by whisking or from an aerosol can. The resulting foam is said to be stable in a temperature range of −8 to 50° C. when using alcohol up to a maximum alcohol content of 40 vol. % and to acid up to a pH of about 2.
U.S. Pat. No. 3,809,764 describes low caloric food compositions comprising an aqueous foam containing water, polyglycerol ester as foaming agent, a hydrophilic colloid as stabilizer and optional ingredients. Example A describes the preparation of a whipped imitation butter that is said to be stable for several days at room temperature.
U.S. Pat. No. 5,000,974 describes aerated food products formed by aerating a fruit base comprising fruit or fruit extract base, locust bean flour, pectin, carrageenan and water. The aerated food products are said to be structure-stable, temperature-insensitive as well as inexpensive.
WO 2006/067064 describes a shelf stable mousse comprising a food composition based on condensed milk aerated with an inert gas, wherein the food composition contains a foam stabilizer and has a fat content of les than 25% by weight. It is stated in the international patent application that the shelf stable mousse does not need to be stored in a refrigerated environment.